Abdominal angiostrongylosis is caused by Angiostrongylus costaricensis Morera & Cespedes, 1971. Over 120 human cases have been studied in Costa Rica. A case has been found in Honduras and there is reason to believe that the disease was founded also in Venezuela. In Panama the parasite has been found in five wild rodents: Sigmodon hispidus, Rattus rattus, Zygodontomys microtinus, Liomys adspersus & Oryzomys fulvescens. The intermediate host, Vaginulus (Sarasinula) plebeius is a slug very common in Costa Rica. Because of the importance of this new human parasitic disease, the follow epidemiological aspects of the problem should be studied: 1. Geographical distribution in Costa Rica. 1.1. in rodents (definitive host); 1.2. in molluscs (intermediate host). 2. Methods. 2.1. Investigation of L1 of A. costaricensis in feces of rodents; 2.2. Search of L3 of A. costaricensis in molluscs.